And loading times are quite bad (10 times slower - compared to firefox or chrome pdf viewers).
Which is what I guess you mean about 10x slower -- so you're making an unfair comparison as you're counting the network at peak, whereas browser plugins load from disk or memory.
But I actually thought the load of the PDF (once the app was loaded) was, for MuPDF.js, slightly faster than the browser plugin. When I watched it, tho I have not benched it. Do you have any benchmarks?
As others in the thread also report significant speed gains I think you either have some weird issue with your setup or how you measure performance.